TempSeal Masking. Image Credit: Ellsworth           Masking Liquid. Image Credit: Grainger

Stop offs and masking compounds are used to prevent coatings, braze, solder, adhesive or paint from sticking to a region of a part such as threaded areas, seal surfaces or areas not part of the joint or not requiring environmental protection.

Product Type

Stop off coatings and masking compounds have slightly different functions.

• Stop off coatings- Are used to prevent braze or solder from flowing over and sticking to a region of a part such as threaded areas, seal surfaces or areas not part of the joint. Stop off also prevents parts from being joined accidentally during furnace brazing or soldering. The coatings are also used to prevent carburization, nitridation, galvenization, and other high temperature metallurgical coatings or treatments on specific regions of a part. Stop offs are high temperature coatings applied by brushing, spraying or dipping. After thermal processing, the stop off is brushed and/or washed off the surface.

• Masking compounds- Are used to prevent paint, adhesives, sealants, sealers, primers, and other coatings from sticking to a region of a part such as threaded areas seal surfaces or other areas of the part not requiring environmental protection. Masking compounds are also applied to spray booth surfaces, coating hooks, and coating fixtures to prevent coatings from sticking and/or to allow easy removal of coating build-up after several coating process cycles. Masking compounds are coatings applied by brushing, spraying, or dipping. After the paint dries or the coating cures, the masking layer is peeled, brushed and/or washed off the surface. Masking compounds enable selective coating of surfaces for generating patterns, numbering, lettering, signage, texturing or decorative surfaces with multiple colors, gloss levels or appearances. Screen coating also uses a masking compound to block regions, which are not to be printed. Rubber, rubberized or elastomeric masking compounds are used in abrasive blasting or peeling applications to allow selective material removal or surface treatment of glass, wood and metal surfaces. Masking compounds are also used in photochemical or chemical milling processes. In photochemical processing, selective regions of a surface are protected by a mask coating while the unmasked regions are then etched to selectively remove material.

Selection Guide

GlobalSpec allows industrial buyers to select stop off coatings and masking compounds based on several features including technology, materials, processing, performance, product features, form, and applications. Some of these options will be described in more detail below.

Technology

Stop off coatings and masking compounds employ different technologies depending on the intended application.  

• Film drying/air setting forms a continuous, dry film from a binder which can be pigmented. The evaporation of the solvent, carrier, or thinner sets the coating.
• Multicomponent coating systems use a polymeric protective film that applies a prime coat, intermediate coat, and/or finish coat.They can consist of multiple liquids (A+B or A+B+C) that are blended together just before an end-use application. Some of the components can be catalysts, curing agents, retarders, accelerators, fillers, reinforcements, colorants, or specific property enhancers.
• Reactive / moisture cured resins are single-component adhesives that are applied in the same way as hot melt adhesives. The resins react with moisture to crosslink and polymerize, resulting in a cured material. Polyurethane reactives (PUR) are examples of reactive resins. Certain silicones and cyanoacrylates also react with moisture or water to cure the adhesive or sealant.
• Thermoplastic coatings are powders that melt repeatedly when heated. They solidify when cooled.

• Thermoset coatings are powders that undergo a chemical reaction during the cure cycle when heated.

• UV Irradiation / radiation cured coatings are cured through ultraviolet (UV), electron beam, or other irradiation.

Form

Form is used to describe the delivery mechanism for the stop off coating or masking compound.